Abrasive bonding alloy



Patented Jan. 16, 1 945 2,ss1.4o1

ABRASIVE BONDING ALLOY Hermann Kott, West Orange, N. J., assignor to Fish-Schurman Corporation, New York, N. Y., a corporation of New York No Drawing. Original application December 28,

1943, Serial No. 515,972. Divided and this application April 18, 1944, Serial No. 531,647

4 Claims.

This invention relates to metallurgy and more particularly to powder metallurgy and has for its object the provision of a mixture of metal powders which is characterized by a relatively low shrinkage constant on sintering, a high density and a high resistance to corrosion and to surface oxidation or rusting as well as a surface physical characteristic known in the art as "slipperiness."

Another object is to provide a mixture of metal powders which on mold sintering under relatively light pressures sinters together to a dense metallic structure characterized by high strength and ductflity, rust-resistance and by a surface possessing the property of "slipperiness."

different shrinkage constants. I have found, however, that for most purposes a shrinkage constant of about 2% is most generally utilizable and to obtain thisshrinkage constant Mn or Ni or Mn and Ni in combination should approximate 5%.

The metals Cu, Au and Ag are, for the purpose of this invention, also substantial equivalents and to obtain the desired result of rust-resistance by the use of these metals I have found that in most instances from .20 to 30% of one or more of these metals is suflicient although largeramounts up to 1% may be employed to accentuate this property, if desired, and to increase the resistance of the alloy to surface oxidation.

Other Objects will be apparent asthe invention is more fully hereinafter disclosed.

This application is a divisional application of my application Serial No. 515,972, filed December 28, 1943, which application is assigned to the same assignee as the present application.

In accordance with the above objects I have discovered that a mixture of metal powders con-- sisting of 3 to of one'of the metals Mn and Ni, small amounts up to 1% of, at least one of the metals Cu, Au and Ag, small fractional percentages of indium, balance an iron-carbon alloy containing about the eutectoid percentage of carbon (.87% C), when mold sintered under relatively light pressures at temperatures within the range 725800 C., sinters together with relatively low shrinkage into a dense metallic structure characterized by high strength and ductility, excellent rust-resistance, and by a surface physical property known in the art as fslipperiness."

This combination of properties particularly adapts the metal powder mixture to wide use in the art of powder metallurgy in the forming of a plurality of products, as one skilled in the art will readily recognize.

In the above mixture of metal powders, the metals Mn and Ni appear to impart the low shrinkage properties as well as to improve the strength and ductility to the sintered iron-carbon alloy.

The metals Cu, Au and Ag, appear to in art increased density and rust-resistance to the sintered iron-carbon alloy and the metal indium appears to impart increased rust-resistance and 5 the surface characteristic. oi slipperiness."

In the practice of the present invention, Mn

' and Ni are substantial equivalents, one for the.

other, and may be employed singly or in combination as may be desired to obtain a plurality of In most instances I prefer to employ mixtures of the metals Cu, Au and Ag. Gold and silver in approximately equal amounts and in total amount approximating .20% have been found to be particularly eifective in imparting rust-resistance properties to iron-carbon-manganese mixtures containing '.87% carbon and 5.0% Mn. Copper, when used alone, must be employed in somewhat higher amounts to obtain substantially equivalent rust-resistance in this iron-carbon-manganese mixture, for example Gold and silver, each when used alone' appear about equally effective to produce substantially equivalent rust-resistancepropertles in the iron-carbon-manganese mixture when used in amounts approximating 25%. Gold and copper and silver and copper mixtures, each in equal amounts, appear slightly less effective in imparting rustresistant properties to the above iron-carbonmanganese mixture than either gold or silver or .the 50-50 mixture of gold and silver.

The metal indium is primarily employed for- D the purpose of imparting the surface characteristic of slipperiness and preferably is used in the minimum amount necessary to impart this prop erty. This will vary somewhat with variation in the amount of the metals Cu, Au and Ag, employed and where the amount of these metals I is held to the minimum amounts required to impart rust-resistance to the sintered alloy, I have found that indium in amounts as low as .10% imparts pronounced surface slipperiness properties to the sintered iron-carbon-manganese alloy above identified.

In addition to imparting surface, slipperiness to the sintered alloy the metal indiumalso functions as a hardening agent for the metals Cu.

' Au and Ag.

As a specific example of the present invention,

combinations of metal powder mixtures having described with respect to a combination of these metal powders found most suitable for'use in the sinter forming by powder metallurgy of a metal lic abrasive composition of matter, such as an abrasive tool, consisting of the metallic mixture of the present invention impregnated with diamond fragments.

In th manufacture of metallic abrasive compositions by powder metallurgy the general practice is to form a mixture of diamond fragments and metal powder, compact the mixture to desired size, shape and configuration, and then to heat-treat the compacted mixture at an elevated temperature at which the metal powder of the mixture will sinter together into a metallic structure of the requisite density and strength.

In co-pending application Serial No. 488,566, filed May 26, 1943, which is assigned to the same assignee as the present invention, I have dis-' closedand claimed an abrasive composition of matter comprised of diamond fragments dispersed throughout a sintered metallic matrix consisting of an iron-carbon alloy containing about the eutectoid percentage of carbon (.87% C) which is characterized by having the diamond fragments surfaced with a mechanically adherent relatively thin film coating of a platinum group metal, specificall rhodium. The mechanically adherent thin film coating of the platinum group metal in this combination of materials functions to protect the surface of the diamond from oxidation during heat-treating and from solution-reaction with the metal powders during heat-treating and to alloy bond the diamond in position within the sintered metal body.

In the practice of the specific embodiment of the present invention, diamond fragments surfaced with a platinum group metal, such as rhodium, are also preferred, and such metal surfaced diamond fragments are mixed with'the metal powder mixture of the present invention and the mixture is mold sintered together to form a metallic abrasive composition of matter, such as a grinding or abrading tool.

In the forming of a grinding or abrading tool of such an abrasive composition of matter, the

most essential requirement for the metal powder mixture employed is that of low shrinkage constant under relatively light pressures. This is obtained, .in accordance with the present invention by using a mixture consisting of iron, carbon and manganese, containing carbon about .8'7% and manganese about 5%.- This mixture following molding compaction under very light pressures may be heat-treated at temperatures within the range 725-800 C. to sinter the same into a metallic structure of high density without shrinking more than about 2%.

This low shrinkage constant under. relatively light pressures is particularly advantageous in this field of utility in that pressures less than that perforating the relatively thin film platinum group metal coating on the surface of the diamond fragments may be employed in forming the particular abrading tool desired, thereby protecting the diamond from solution-reaction with the metal powders during sintering.

Additions of at least one of the metals Cu, Au and Ag,'to the Fe.C.Mn metal powder mixture, preferably a -50 mixture of the metals Au and Ag in total amount approximating 20% and of the metal indium in an amount approximating .10%, each in substitution for an equivalent amount of the iron-carbon alloy base, provides a metal powder mixture which on sintering possesses also the properties of rusteresistance and surface slipperiness as well as increased density, strengthand ductility.

As a specific example:

The preferred mixture of metal powders for use in the forming of an abrasive tool consists of .10% Au, .10% Ag, .10% In, 5% Mn and the remainder carbonyl iron powder having a carbon content approximating 37%. The particle size of the carbonyl iron powder is, preferably, extremely small and should contain no particles larger than about 400 mesh. The particle size of the Mn-may be considerably larger than this, but preferably should be less than about 200 mesh. The particle size of the Au, Ag and In should be as small as possible and should at least pass 200 to 300 mesh, in order to facilitate the substantially uniform dispersion of the same throughout the iron metal powder.

This mixture of metal powders, after thorough mixing, for example, in a ball mill for an extended time interval, is then mixed with the rhodium-surfaced diamond fragments, in the desired relative amounts which varies somewhat with respect to the particle size of the diamonds. The diamond-metal powder mixture thus obtained after being disposed in a mold with slight tamping or compaction sufficient to eliminate any large voids and to level off the material in the mold, may then be heated, under substantially non-oxidizing conditions on a slowly rising temperature gradient to a temperature approximating 750 C. for an extended time interval to sinter the same to a coherent metallic body, care being taken during the early stages of heating to heat quite slowly to drive off any moisture and surface adsorbed gases from the metal powders-before sintering.

' One of the major advantages of the present metallic composition over the iron-carbon alloy of the said co-pending application, lies in the fact that because of the relatively low shrinkage constant of the present composition and relatively high strength and ductility of the same, the amount of diamond fragments incorporated in the mixture may be materially increased, thereby obtaining more diamond fragments per unit surface area than heretofore obtainable.

As an example, where diamond fragments having a particle size passing mesh, but not passing mesh, are employed, the ratio of diamonds to metal powder may be as high as 1 to 3 whereas with the iron-carbon alloy alone a ratio of 1 to 10 is about ashigh a ratio as may be used. This results in a cutting or abrading surface of greatly increased efficiency. I

In the above specific example, nickel may be substituted in part or in whole for the manganese. In general, nickel is more effective than manganese and may be used in lesser amounts.

For example, 2 to 3% Ni appears to be equivalent :to 5% Mn. Preferably, carbonyl nickel powder is employed.

In the above specific example, the metals gold and silver may be displaced by .25% of either gold or silver or .35% Cu or with about .30% of a 50-50 mixture of either' Cu and Au or Cu and Ag without essential departure from the invention. Also, indium in amounts greater than .10% and up to .30% may be employed without departure.

Following sintering, I prefer to quench the sintered metal product in cold water to harden the same and to prevent oxidation of the protruding edges of the diamond fragments.

As an illustration of the non-shrinking prop 2,867,407 erties of the metalcomposition of the present invention, various tests have shown that the shrinkageof the metal composition of the specific example given approximates 2% when no compacting pressure is applied to the metal powder in the mold prior to heat-treating. This low shrink-' subsequently even at quite elevated temperatures,

indicates also that thesintered alloy composition of the present invention has a relatively low coefiicient of expansion.

To facilitate the removal of the sintered metallic body from the mold after sintering, the interior surface of the mold is covered with refractory material such as silica dust, graphite, aluminum oxide, and the like.

It is believed apparent from the above disclosure that the present invention may be widely modified without essential departure from the same and all such modifications and adaptations are contemplated as may fall within the scope of the following claims.

What I claim is:

1. A rust-resistant metallic composition of matter comprised of a sintered mixture of metal powders consisting of a fractional percentage of at least one of the metals of the group consisting of Cu, Au andAg, a small fractional percentage of indium, from 3 to 10% of one of the metals Mn and Ni, balance iron containing the eutectoid percentage of carbon.

2. A rust-resistant metallic composition of matter comprised of a sintered mixture of metal powders consisting of from .20 to at least one of the metals CU, Au and Ag, .10% to .30%

y In, 3.0 to 10% one of the metals Mn and Ni,

balance Fe containing about .87% C;

3. A rust-resistant metallic composition of matter comprised of a sintered mixture of metal powders consisting of from .20 to .35% at least one of the metals Cu, Au and Ag, .10% to .30% In, 5.0% Mn, balance Fe containing about .87% C. v 4. A rust-resistant metallic composition of matter comprised of a sintered mixture of metal powders consisting of .20%-Au and Ag in about equal amounts,'.l0% In, 5.0% Mn, balance Fe containing about .87 C.- v

HERMANN KOTT. 

